1. Field of the Invention
The present invention relates to a light emitting device.
2. Related Art
As a light source of a general lighting equipment or a vehicle headlight, an incandescent lamp, a halogen lamp, or a discharge lamp has been widely used. Recently, from a viewpoint of global warming prevention and long-term lifespan, a semiconductor light emitting element, such as a LED (Light Emitting Diode) and an organic EL (Electro Luminescence), has been used (for example, refer to Patent Document 1 and Patent Document 2).
Patent Document 1: JP-A-2010-123605
Patent Document 2: JP-A-2009-206294
Since the semiconductor light emitting element has a low light emitting efficiency, it is necessary to mount a plurality of light emitting chips, in order to utilize the semiconductor light emitting element, for example, as the light source of the vehicle headlight. As a result, there was a disadvantage that a manufacturing cost is increased.
Accordingly, in the light emitting device using the semiconductor light emitting element, particularly, in the light emitting device that is used for the vehicle headlight, it is important to improve a light emitting efficiency and a light density (luminance) in order to properly control a light distribution, in addition to an increase of an entire light quantity of the light emitting device.
As the light emitting device using the semiconductor light emitting element, a light emitting device that emits white light is widely used. In the light emitting device that emits white light, for example, a semiconductor light emitting element that emits blue light (that is, a blue light emitting diode) and a wavelength conversion layer (e.g. a yellow phosphor layer) that is excited by the light emitted from the semiconductor light emitting element are provided. In the light emitting device, yellow light is excited as a result that a part of the blue light is absorbed in the phosphor, and the blue light that has passed through the wavelength conversion layer and the excited yellow light are mixed to emit pseudo white light to outside.
Accordingly, in the light emitting device using the semiconductor light emitting element and the wavelength conversion layer, it is important to emit light without color non-uniformity to outside as an illumination light by properly mixing the light emitted from the semiconductor light emitting element and the excited light.
In the light emitting devices described in Patent Document 1 and Patent Document 2, a semiconductor light emitting element is arranged in a concave portion. Light emitted from the semiconductor light emitting element and directs sideward is reflected on an inner peripheral surface (reflection surface) of the concave portion, and the light is guided to an open surface side of the concave portion to emit the light to the outside.
If the reflection surface is perpendicular to the emitting surface of the semiconductor light emitting element, repeated reflection of the light would occur and a loss of light through heat would occur. Accordingly, in the light emitting devices described in Patent Document 1 and Patent Document 2, the reflection surface is inclined outwardly as it goes in an emitting direction so as to approximate a reflection direction to the emitting direction and to improve the light emitting efficiency.
However, in the light emitting devices described in Patent Document 1 and Patent Document 2, since the reflection surface is inclined to be displaced to the outside as it goes in the emitting direction, the open surface of the concave portion that is an exit surface of the light has a large area, and thus the density (luminance) of the emitted light becomes lowered.
Further, since the concave portion is formed to be expanded as it approximates the exit surface, the quantity of the blue light emitted from the emitting surface of the semiconductor light emitting element and reaches the outer peripheral side of the concave portion is decreased, and an amount of the blue light with respect to the yellow light is decreased. As a result, a proper mixing of the lights is not performed, and this may cause the color non-uniformity to occur.